I. Field of the Invention
The present invention relates generally to a liner for a waterway to minimize water loss through ground absorption.
II. Description of the Prior Art
Water or irrigation canals are used extensively in the southwestern portion of the United States for conveying water from the source of the water to a water processing plant. From the plant, the water is ultimately distributed to the end users.
These previously known canals typically comprise little more than a trough excavated through the land and through which the water flows. One disadvantage of these previously known canals, however, is that a great deal of water is lost through ground absorption. Such loss of water through ground absorption is unacceptable, especially during prolonged drought conditions.
One recently devised method for minimizing the loss of water through ground absorption involves laying a liner of a geomembrane material along the bottom of the canal. This liner is then held in place, as well as protected, by a cementious material which overlies and protects the liner. Furthermore, both the liner, as well as the cementious layer, are laid along the bottom of the canal while the canal is in use and thus at least partially filled with water.
In order to feed the liner so that it covers the bottom of the canal, a machine has been developed having a pair of spaced apart guide rails which slidably engage opposite sides of the sheet which forms the liner. Typically, these guide rails include a hollow interior having a longitudinally extending slot which extends along the length of the guide rail. A strand enclosed in a flap along the edge of the sheet is then positioned within the interior of the guide rail and is longitudinally slidable with respect to the guide rail.
One disadvantage of these previously known constructions, however, is that the flap was typically solvent welded around the strand and that the strand was relatively small in size. This, in turn, resulted in two problems.
First, there was a tendency that the strand would pull out of the channel slot when the sheet was subjected to lateral stress or tension. Even more serious, however, was that the solvent weld between the flap and the PVC sheet around the strand would fail under stress.
A still further problem arose when it was necessary to use a third guide rail positioned in between the outer two guide rails in order to guide the liner to the bottom of a canal. In order to secure a strand to the center of the PVC sheet, the strand was positioned along the sheet, the sheet wrapped around the strand and then secured together by solvent welding.
One disadvantage of this previously known method for securing a center guide strand to the sheet was that the solvent welding would fail when the sheet was subjected to lateral tension. This in turn can cause improper feeding of the liner into the canal and even possible jamming of the machine.